Reputation of a social entity (a person, a social group, an organization) is an opinion about that entity, typically a result of social evaluation on a set of criteria. It is important in business, education, online communities, and many other fields. Reputation may be considered as a component of identity as defined by others. Reputation is known to be a ubiquitous, spontaneous, and highly efficient mechanism of social control in natural societies. It is a subject of study in social, management and technological sciences. Its influence ranges from competitive settings, like markets, to cooperative ones, like firms, organisations, institutions and communities. Furthermore, reputation acts on different levels of agency, individual and supra-individual. At the supra-individual level, it concerns groups, communities, collectives and abstract social entities (such as firms, corporations, organizations, countries, cultures and even civilizations). It affects phenomena of different scales, from everyday life to relationships between nations. Reputation is a fundamental instrument of social order, based upon distributed, spontaneous social control.